1. Field of the Invention
The present invention relates to a composition for use in the cooling systems of internal combustion engines. The composition is an ethylene glycol-based antifreeze composition which is designed to protect aluminum water pumps, aluminum engine heads, and aluminum radiators from corrosion.
2. Description of the Prior Art
Water is generally accepted heat exchange medium for the cooling systems of internal combustion engines. Ethylene glycol is widely used to lower the freezing point of water and to raise its boiling point to enable the coolant to be used over a wider range of temperatures. However, ethylene glycol and other such antifreezes tend to corrode the metals from which the internal combustion engines are made under the condition of elevated temperature and aeration. Therefore, it has been necessary to add corrosion inhibitor compositions to the antifreeze solutions to lessen the corrosive effect of the solutions. (P. Weissler, Automotive Cooling Journal 26, 34 (1983))
Numerous corrosion inhibitors have been prepared to date. Such inhibitors include both organic materials and inorganic materials. Illustrative of organic materials that have been used in anti-freeze compositions are: guanidine, citrates, coal tar derivatives, petroleum bases, thiocyanates, peptones, phenols, thioureas, tannin, morpholin, triethanolamine, tartrates, organic nitrites, mercaptans and nitro-compounds. Illustrative of the inorganic materials that have been used in anti-freeze compositions are: sulfates, sulfides, the alkaline metal chromates, nitrites, phosphates, molybdates, vanadates, tungstates, borates, and silicates.
The corrosion inhibitors formulated in anti-freeze compositions should adequately retard corrosion of metals such as cast aluminum, cast iron, steel, copper, solder, and brass used in cooling systems and engines. Some inhibitors inhibit the corrosion of some metals but are not particularly useful in inhibiting the corrosion of other metals. Antifreeze compositions should not also attack or swell rubber hoses that are part of the cooling systems. Besides electrochemical oxidation, air cavitation causes the corrosion of the metals. Several inhibitors of organic and inorganic materials should be formulated at the same time in the anti-freeze compositions to meet metal corrosion protection requirements. Since anti-freeze compositions containing two or more phases entail dispensing and handling problems, it would be most desirable if such inhibited anti-freeze compositions were single phase systems.
In recent years, automobile manufacturers have been using more and more aluminum as a lightweight material in the construction of the internal combustion engines. Alkaline metal borates known as good corrosion inhibitors for cast iron engines do not provide good protection for aluminum (Japanese Patent 49-5509). It is known that alkaline metal silicates are effective corrosion inhibitors for aluminum alloys. It has therefore been desirable to use alkaline metal silicates in anti-freeze formulations. However, alkaline metal silicates tend to form gels in alkylene glycoles which are normally used as anti-freezes. M. C. Abel reported that gelation problem could be solved reducing the silicate amount under 0.08% and maintaining the pH of the composition between 9 and 11 (U.S. Pat. No. 4,426,309). Since aluminum is amphoteric, it will easily corrode in either strongly acidic or basic medium. Thus, it has been previously proposed to use a stabilizer to prevent the gelation of the alkali metal silicate in the antifreeze composition.
Several types of silicon compounds have been described as suitable stabilizers. For instance, U.S. Pat. Nos. 3,234,144 and 4,241,012 describe the use of amino-siloxanes as stabilizers; U.S. Pat. Nos. 3,3126,222 and 4,241,011 disclose carboxy siloxanes as suitable stabilizers; and U.S. Pat. Nos. 3,337,496 and 4,210,548 recommend the use of hydroxyalkyl derivatives of siloxanes. Resently hydroxyl and carboxy or cyano groups substituted organosilanes have been reported to be suitable as the stabilizers (U.S. patent application Ser. No. 180,489 filed Apr. 12, 1988)